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Spongy rear pedal after bleeding.

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NJD
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PostPosted: 21:57 - 30 Mar 2018    Post subject: Spongy rear pedal after bleeding. Reply with quote

Last Sunday I over tightened the rear caliper banjo bolt attempting to tighten it (spaz episode) and had to leave it three days (Monday, Tuesday, Wednesday) before I could get all the parts delivered to perform a rebuild (I'd took it apart on that Sunday to have a look and clean it up but was worse than expected: caliper seal was fudged). During that time the Banjo bolt (the thread, since the head had snapped off) was in the caliper and the hose had a bag over the end (to prevent moisture entering).

Yesterday -- Thursday -- I rebuilt the caliper and bled the brakes. I had to remove all the fluid with a tissue (there wasn't much left as was given I'd lost some the Sunday prior pushing the pistons out) to clean the resivour because it had dirt on the bottom that I didn't want to suck into the line. While bleeding the brakes it started to rain lightly and so I put a cover over the top of the bike to prevent rain from enterting the brake resviour (I mention this because I assume rain can contaminate fluid). Satisfied that the fluid was clear and bubble free I tightened everything up and left it to use today, Friday.

And as I found out today the rear pedal was spongy. The brake is there but it's soft and so I can only assume there's still some air in the lines. I'd say the pedals so soft that its dangerous to use (says the one who still rode it to and from work like a donkey).

The fluid I used to bleed the brakes was opened last Sunday and put back in the cupboard, with a lid on, and used on Thursday. Is brake fluid really redundant after three days? I ask because I want to eliminate this as a cause. The fluid did had small air bubbles in when looking into the bottle but I've read people recommending six months before throwing a bottle away and so just want to eliminate this. Ie: if I bleed them again is this fluid ok to use or do I use the new bottle I've just purchased.

I used copper washers from Wemoto on the Banjo put think I'll probably replace them for ones I've got from Halfrauds (in a set) since they formed a better seal (why I didn't use them in the first place I'll never know).

The brake line has been on the bike since I've got it but I don't suspect it to be at fault as has the bleed nipple on the caliper.

My guess is I didn't bleed it for long enough but want to clarify on the fluid issue and gain a second opinion before I go any further.

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Shaft
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PostPosted: 22:38 - 30 Mar 2018    Post subject: Reply with quote

It's not your fluid, look for another cause.
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Hong Kong Phooey
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PostPosted: 22:51 - 30 Mar 2018    Post subject: Re: Spongy rear pedal after bleeding. Reply with quote

NJD wrote:


My guess is I didn't bleed it for long enough but want to clarify on the fluid issue and gain a second opinion before I go any further.

Thumbs Up


I always use a one way valve bleeding kit, it's much faster and removes any doubt - you can see the colour of the fluid in the tube so you know when it's flushed through.

Cheap - much cheaper than wasting another botte of fluid.

If you really are that tight then use a jar and suitable sized hose. Laughing
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NJD
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PostPosted: 22:59 - 30 Mar 2018    Post subject: Re: Spongy rear pedal after bleeding. Reply with quote

Hong Kong Phooey wrote:
I always use a one way valve bleeding kit


I did, too. I've done this once before and didn't have any trouble (well, twice if you count bleeding both the front calipers).

Here's a cheap one if anyone has this job on the horizon.

..

Now I know fluid isn't to blame I suspect -- looking at pictures from the last time I did this -- that I may have put the rubber seal on the rear master cylinder back on the bike incorrectly. I remember last time I finished the job, looked at the manual and had to go back out to put it in the correct way.

Going to bleed it some more on Sunday and make sure I get the cylinder seal put on correctly. Thumbs Up

..

1) https://s7.postimg.org/ou7rn5vej/image.jpg
2) https://s7.postimg.org/61vwjlm5n/image.jpg
3) https://s7.postimg.org/61vwjltvf/image.jpg
4) https://s7.postimg.org/z4a6mf0pn/image.jpg

^ They're from last time, reference for Sunday -- and anyone who may need them in the future.
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NJD
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PostPosted: 13:10 - 01 Apr 2018    Post subject: Reply with quote

Done, I think.

Used the method: "press pedal several times and hold, open bleed valve and watch fluid rush out for a moment or two, close bleed valve and release pedal." Pedal felt solid after not very long.

Went for a quick ride and the pedal seemed fine although I think the bike could do with a longer run or some constant use to wake it up a little. Probably developed "play too much attention to something after a fault occurs" syndrome, though, so will see what the commutes to work bring.

Everything -- beside the clips that attach onto the hose going from the M/C to behind the real pedal bracket (they're rusty) -- is in good shape. If further fault occurs there's either an air leak somewhere or it could be as simple as road crud accumulating behind the pedal bracket.

Here's hoping to end of it. Laughing
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Howling Terror
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PostPosted: 14:07 - 01 Apr 2018    Post subject: Reply with quote

...and to push those last few micro bubbles out tie the lever down. Depending on bike you may be able to use a piece of wood to brace against the frame or anchor the lever down. Fiddly but will push the bubbles out.
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tom_e
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PostPosted: 14:28 - 01 Apr 2018    Post subject: Reply with quote

Howling Terror wrote:
...and to push those last few micro bubbles out tie the lever down. Depending on bike you may be able to use a piece of wood to brace against the frame or anchor the lever down. Fiddly but will push the bubbles out.


I used a a weight plate put the lever peg through the bar hole. Easy and effective if you've got any lying around.
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fireyphoenix1...
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PostPosted: 16:42 - 01 Apr 2018    Post subject: Reply with quote

Same as what i do after a brake bleed. When i park it up, zip tie the front brake on, zip tie a weight to the rear.
Leave it over night and by morning all the last tiny bits of air have worked free.
Nice solid feeling lever with no "squish" to it.
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NJD
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PostPosted: 18:01 - 01 Apr 2018    Post subject: Reply with quote

Things they don't teach you while learning to ride a motorbike tip 101: physical books do have a use, after all (try doing this with your kindle, huh).

Hopefully remains in place until tomorrow morning (several hours is better than non, right?).

https://s7.postimg.org/w932flge3/R1_DX.jpg

https://s7.postimg.org/uiomra3i3/R1_D.jpg
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MCN
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PostPosted: 10:13 - 11 Apr 2018    Post subject: Reply with quote

Micro-bubbles.

Non-Micro-bubbles can be pushed out a system as they are big enough to see and connect together and make bigger bubbles.

Compressing a fluid will force any Micro-bubbles to become smaller and possibly become dissolved in the solution.
When any pressure exerted that compressed them is removed the micro-bubbles will return to their previous state.
If you have a concern about micro-bubbles then perhaps more scientific approach would be to create a low-pressure state (vacuum-ish). Doing that will allow the micro-bubbles to become larger and join up to form bigger bubbles.
When normal atmospheric pressure is restored then any big bubbles that have formed can be pushed out by bleeding.

😁
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kgm
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PostPosted: 12:26 - 11 Apr 2018    Post subject: Reply with quote

As an aside I've used fluid from a bottle that was opened a few months previously in an emergency and had no problem getting a properly solid feel.
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MCN
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PostPosted: 18:16 - 11 Apr 2018    Post subject: Reply with quote

kgm wrote:
As an aside I've used fluid from a bottle that was opened a few months previously in an emergency and had no problem getting a properly solid feel.


Should've kept that under your hat Big Yin. Shocked

There will be a hail of criticism for your lack-a-daisy-cal approach to maintenance now.

You have been warned.

Very Happy
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kgm
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PostPosted: 19:09 - 11 Apr 2018    Post subject: Reply with quote

MCN wrote:

Should've kept that under your hat Big Yin. Shocked

There will be a hail of criticism for your lack-a-daisy-cal approach to maintenance now.

You have been warned.

Very Happy


Probably. I was reluctant to do so but in the end it caused no issue at all and it was fine till the next change a few months later. Not something I'd make a habit of but ok in a pinch.
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kramdra
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PostPosted: 20:40 - 11 Apr 2018    Post subject: Reply with quote

MCN wrote:
Micro-bubbles



Or incompetence. Read the opening post again. If you follow a process and fill/ bleed in a specific order, you can have it done perfectly in about 5-15 minutes, repeatable every time.
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NJD
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PostPosted: 21:31 - 11 Apr 2018    Post subject: Reply with quote

kramdra wrote:
incompetence.


Rated funny because you've never got anything wrong, ever. Rolling Eyes
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MCN
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PostPosted: 22:32 - 11 Apr 2018    Post subject: Reply with quote

kramdra wrote:
MCN wrote:
Micro-bubbles



Or incompetence. Read the opening post again. If you follow a process and fill/ bleed in a specific order, you can have it done perfectly in about 5-15 minutes, repeatable every time.


I hope you are not being an arse.

And you are just trying to explain something incompetently.
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